Container closure



Dec. 31, 1946. w. c. KESLER ETAL. 2,413,453

CONTAINER CLOSURE Filed Nov. 24, 1943 .Ezbpniors: wzziamc. Kazan i,

Wai (H. Ryan Patented Dec. 31, 1946 Md., assignors to Crown Cork & Seal Company, Inc., Baltimore, Md., a corporation of New York Application November 24, 1943, Serial No. 511,616

1 Gla.im. (Cl. 215-40) This invention relates to container closures notably crown" caps for sealing pressure beverages. Such a cap includes a metal shell, and a cushion liner positioned therein, usually of cork or cork composition, The liner provides the required compressibility and resilience to assure that the cap will form a substantially permanent, leak-proof seal with the lip of the container to which it is applied by a crowning pressure generally of the order of about 700 pounds or more.

The primary object of this invention is to provide a cap with a cushion liner of paper board having compressibility and resilience comparab to the customary cork liner.

Another object of the invention is to provide a cap in which the paper board liner has critical characteristics of (a) thickness, (b) apparent density and (c) proportions of fibres, which each contribute to the effectiveness of the closure sealing element.

A further object of the invention is to provide a method of preparing the liner material wherein the fibres are beaten to have a critical range of hydration or freeness to the end that a prdnot having uniform sealing properties is obtained.

In carrying out the invention, a preferred stock consists of a mixture of sulfate (kraft) pulp and waste (or overissue) news,

The proportions of the mixture are critical for a satisfactory liner and comprise substantially 15 to 25% kraft pulp and substantially 85 to 75% waste news. Within this range a. liner is produced which is neither too compressible or too hard for cap sealing purposes.

Similar attention to the critical proportions recited should be given in the case of other equivalent mixtures'of fibres which may be used.

The fibres are mixed with water and are heaten and thereby become hydrated, i. e., take up water, and the degree of hydration increases with the length of time of beating. Up to a certain point, the beating increases the strength but, more particularly, the resilience of the fibre. We find the amount of hydration to be critical and We accurately measure the same by a standardized method known as the Schopper-Riegler wherein the hydration is expressed as the number of cc. of free water. Hereinafter, the hydration will be stated in terms of co. freeness." The freeness decreases as the hydration increases, and hence, the lower the freeness, the degree of hydration.

We have discovered that the critical limits of "freeness" of the fibres above mentioned for a higher the preferredv liner material are between about 544 cc. and about 736 cc. (free water on the Schopper-Riegler 2 gram-1,000 cc. test), the outside critical limits being between substantially 525 cc. and 765 cc.

The difference in time required to obtain a prescribed freeness on kraft and waste news is so great that each stock is preferably beaten separately to the required freeness, and mixed after beating. We find in practice that when the stocks are beaten together to the required freeness, the kraft pulp is under-hydrated and the news is considerably over-hydrated, so that the resultant board is unsatisfactory. Pulps cannot and should not be beaten fora prescribed time because the time required to reach a prescribed freeness varies in the different pulps and in the same pulp from the same mill. Two pulps will rarely, if ever, beat in the same time, especially if they contain different amounts of Water. Hence bea ing to a prescribed freeness is a critical consi eration.

It is necessary to beat each pulp separately, but it is not necessary to beat each pulp to the prescribed freeness of the final mixture. One pulp can be beaten toward the high freeness (736 cc.) and the other toward the low freeness (544 cc.) and when they are mixed, the freeness of the final mixture will fall between the prescribed limits. Boards made in this manner are quite satisfactory.

The heating of the pulps to our prescribed freeness" limits represents a magnitude of hydration not heretofore carried out in board making. We regard this step of controlling hydration (or freeness) to be critical in insuring the correct compressibility and, especially, resiliency.

The original thickness" of the prepared board, 1. e., the thickness of the liner before being subjected to sealing compression is important as evidenced by our discovery that a sealing liner of kraft-news pulp'stock having a thickness of between about 0.049" and 0.063" is uniformly successful, whereas when these critical limits are departed from and the liner made thicker or thinner, it was not useful as a sealing member.

Apparent density. of the prepared board, namely, the weight per unit volume and expressed as the weight in pounds per square yard per pointof thickness is also a critical consideration. A point" of thickness is 0.001.

The critical limits of apparent density" for a satisfactory liner are between about 0.019 and 0.027 pound per square yard per point. Outside of these limits the products were unsatisfactory as was demonstrated in the case of the liner made from kraft and waste news.

The apparent density is controlled by the regulation of the pressure on the "press :01 and by the number of plys in the sheet plus one nip of the calender.

We find that 5 and 6 ply sheets give the best results, although a satisfactory board may also be back and hold internal gas pressure without leak ing. All boards falling within the limits prescribed above make satisfactory pressure seals, because they have the proper compressibility and resiliency. compressibility and resiliency are apparent density.

There is no convenient method of measurin resiliency in absolute units when a cap is applied to a container such as a bottle, and, therefore, to measure the compressibility, expressing it in terms of residual thickness, under 700 and 860 lbs. capping pressures, we employed a. female die hollowed out to the exact dimensions-and contour of a standard beverage cap anda male plunger of the exact shape and size of a standard beverage bottle neck. The board disc was inserted in the die and pressure was then applied to the plunger and the thickness was measured while the sample was under pressure. and plunger set-up permitted compressingthe material in a laboratory test exactly as it is compressed in commercial capping.

In making the test, 47 samples of satisfactory boards were selected which varied over the range of critical limits in freeness, thickness and apparent density above set forth.

We find from these tests'that the critical limits In the accompanying drawing, we have illustrated a crown cap for a "Standard crown beverage bottle and it is to be understood that other types of closure caps are similarly improved by use of the present invention.

Referring to the drawing:

Figure 1 is an elevation of the inside of a crown cap showing the cushion liner assembled therein; and

The die Figure 2 is a section on the line 2 -2 of Figure The cap shown in Figure 1 includes a metal shell 50 having a skirt H, as shown in Figure 2, and formed with crimps or corrugations I2.

In the case of a Standard crown beverage bottle, Standard 26 mm. crown which means that the diameter taken from the inside perpendicular such caps are usually described as 4 wall of the skirt H is 26.7818 mm. or 1.0545 inches. The invention is equallysatisfactory with other types of crowns of both larger and smaller diameters. The cushion liner is in the form of a circular disc l3 and is assembled in the shell and secured thereto in any suitable manner.

In Figure 2, the, cushion liner is shown havin its uncompressed or original total thickness. The exposed surface of the cushion liner l3 has adhered thereto a spot facing I4 of metal foils and coated papers, such as varnished papers, Vinylite coated'papers, Cellophane and cellulose acetate films, chlorinated rubber and rubber hydrochloride coated papers, resin coated papers and the like, and suitable coatings of resistant material such as vinyl resin or chlorinated rubber. This facing 14, in some cases, extends over the-entire exposed surface of the liner so as to give overall coverage.

The critical conditions described above are subject to variation within the limits stated and the lnventionwill, therefore, be illustrated by a simple. example indicating the results when the proportions of fibres are varied within such limits. A stock was prepared from 15% kraft and 85% waste news, another from 20% kraft and 80% waste news, and a third from 25% kraft and waste news. The freeness (amount of hydration)- wasof the order of 666 cc. and the apparent density was 0.0216 in a board of 0 050 inch thickness made on a cylinder paper making machine in each case. Each pulp was beaten separately and mixed. All of the boards made satisfactory cushion liners for crown caps.

Similar favorable results were obtained in the example just given where the freeness was about 544 co. in onecase, and about 525 co. in another.

Likewise satisfactory boards were produced under the aforesaid varying conditions where the thicknesslof. the board was varied from about 0.049 inch to about 0 063 inch.

, Also under the aforesaid exemplified variations board having an apparent density of between substantially 0.019 and 0.027 pound per square yard perpoint of thickness was produced which was successful for cap cushion liners.

While we have referred and prefer a board made on a cylinder, machine, satisfactory boards can be made on a Fourdrinier paper making machine.

Products .prepared in accordance with the present, invention possess compressibility and resilience comparable to liners of natural and compositioncork, and form satisfactory sealing liners for crown and other types of caps.

By sulfate (kraft) pulp we mean the accepted and understood definition of this material as found in the Dictionary of Paper which gives the following definition:

.Kraft is a very strong paper made from unbleached sulfate wood pulp by prolonged boiling under low pressure, thuspreserving strength because the stock has received less drastic chemical treatment. It is smooth, of a characteristic light brown color, strong and flexible and highly resistant to sudden strain; and now also imitated in various ways. The word is also used in many combinations, such as kraft brown, that is, brown wrapping paper made according to this process which in fact is usually understood by theterm krait paper; kraft pulp, a variety of sulfate wood pulp made from spruce, other conifers, for the production of Kraft wrapping paper."

Or as found on page 94 of Butermeister's Chem asiaesa "Km/t (paper) .-Brown paper made from high class sulphate wood pulp. i

By waste (or overissued) news" we mean as defined in the Dictionary of Paper, which states:

"overissue news-Newspapers which have been printed but not circulated by the publishing plant,

hence clean and uncontaminated. Distinguished iroin' iolded "news-that is, unsold newspapers its presence makes the operation of digesters,

smelters, and causticizing plants diflerent from that usual in the older soda process.

There is more or less confusion in the use of the terms sulfate and 'kraft as applied to the process and products. Sulfate may be considtrom news stands--and crumpled news, which is newspaperssegregated from waste gathered from other sources. 0verissue news, grade No. 1. Clean, fresh,

dry overrun and unsold newspapers not over 60 ered a general term applying to any cooking process in which the loss of alkali is made up by adding sodium sulfate, while kraft is that subdivision of the sulfate process in which the pulp is intentionally undercooked in order to produce very strongfiber. The products of the sulfate process vary according to the cooking conditions from dark brown, unbleachable krait fiber, to a soft, easy bleaching stock. Either bleached or unbleached papers made from sulfate pulps range from a coarse, tough, rattly sheet to a soft, pliable, opaque paper depending on cooking treatment and wood. 7

From this description it is plainly evident that all kraft papers are sulfate.

0r taken from page 56 of Classification and Definitions of Paper (1928), Clarence J. West, vice chairman, Committee on Classification of the Technical Association of Pulp and Paper Industry, which states:

"Kraft pulp-Pulp of wood, by a a large number of kinds of wood; process differs from soda process in the addition of sodium sulphide; generally a strong brown pulp.

or from Chambers Technical Dictionary,

which states:

chemical caustic cooking process; used in connection with days old, from newspaper ofilces. Must be free from excessive rotogravure sheets and colored supplements.

Or from the Classification and Definitions of Paper under the section on waste paper dealing with the standard classification for waste paper adopted by the National Association of Waste Material Dealers, which states:

Newspapera-Shall contain dry, clean newspapers, free from all foreign substances not suitable-for the manufacture of paper. 7

Or as defined in the Dictionary of Paper as folded news" and "crumpled news.

Waste or overissue news pulp employed by us "the mechanical pulp resulting from the disintegration or reduction of waste or overissue news as defined above."

- We claim:

A cap having a. cushion liner formed oil a mix- I ture of about 15 to 25% kratt pulp and about to 15% waste news pulp, said liner having a thickness of between about 0.049 inch and 0.063

inch, and an apparent density between substantially 0.019 and 0.027 pound per square yard per point or thickness. v

WILHAM C. KESLER. VICTOR A. RYAN. 

